The present invention relates to a process for removal and recovery of mercury from aqueous media which contain mercury and undissolved solids. More particularly, the present invention relates to a process for the removal and recovery of mercury from chloralkali plant effluent.
Efforts are being made to prevent the loss of mercury to the environment. Some of the mercury lost to the waterways originates in the form of plant effluent, such as the liquid employed in scrubbing stack gases or effluent from chloralkali plants employing electrolytic cells with mercury cathodes.
One of the schemes proposed to eliminate these losses of mercury in aqueous media comprises reducing ionic mercury contained therein to elemental mercury, aerating the medium with an inert gas which entrains the mercury, followed by recovering the mercury from the gas by scrubbing it with a chlorinated brine solution. Such a procedure is not entirely satisfactory as it generally fails to remove effectively the mercury which is present in the medium. The elemental mercury present in the medium prior to the addition of the reductant, tends to coalesce into larger particles which are not very susceptible to vaporization. Even the agitation of the aqueous medium by the aerating gas and the consequent fragmentation of the agglomerated mercury fails to adequately improve the evaporation rate of the mercury. In addition, typical effluents contain undissolved solids on which the mercury, both elemental and ionic tends to adsorb or with which it might somehow associate itself, further impeding its vaporization and entrainment by the aerating gas.
A laboratory procedure for quantitative assay of mercury comprises boiling the sample with excess strong oxidant such as aqua regia for complete digestion of the elemental mercury, followed by reduction of the ionic mercury and aeration of the medium for mercury detection in the gas phase.
It is the object of the invention to provide an improved process for the removal and recovery of mercury contained in aqueous media.